Abstract

We interpret and document Late Cretaceous and Cenozoic reactivation of older structures on the obliquely rifted margin of southeastern Brazil, attributing them to the combined effects of far-field stresses and hot-spot activity. Our conclusions are based on current seismicity, digital topography, fission-track ages, gravity data, regional reflection seismic profiles, and well data. Our results have important implications for risk factors associated with deep-water exploration plays, especially the prolific Early Cretaceous lacustrine petroleum system of the Campos and Santos basins.

Onshore, widespread crustal seismicity indicates a current transpressional stress regime. The Moho is 37-42 km deep, and neotectonic fault-block tilting has resulted in mountain ranges up to 2700 m high and extensive river capture. Based on fission-track data, the mountains were exhumed in the Cretaceous and Eocene. A series of Tertiary continental pull-apart basins, developed during Paleogene right-lateral transtension, became inverted during Neogene right-lateral transpression. Late Cretaceous-Paleogene alkaline intrusions, attributable to the Trindade hot spot, were emplaced along reactivated Neocomian strike-slip faults and transfer zones.

Offshore, current seismicity is widespread across the continental margin. The locus of clastic fan deposition shifted during the Late Cretaceous and Tertiary because of onshore block faulting and drainage reorganization. Cretaceous sedimentary rocks were folded, tilted, eroded, and unconformably onlapped above an inferred Neocomian Moho uplift to produce an accentuated nearshore hinge line. Neocomian transfer zones were reactivated during ongoing sedimentation, accompanied by abundant volcanism and deep-seated folds attributed to lithospheric buckling. In the Campos area, a coastal salient was uplifted and turbidites were redeposited. In general, regional tilting resulted in thin-skinned deformation above Aptian salt.